[linux-lvm] snapshotting to a different volume group
Stephane Chazelas
stephane.chazelas at emerson.com
Fri Apr 18 12:45:40 UTC 2008
2008-04-18 12:53:15 +0100, Stephane Chazelas:
[...]
> By bypassing LVM2 and using dmsetup directly, would I
> theoretically be able to setup a snapshot outside of LVM2
> managed volume groups, is it worth me trying to dig that way?
> Something like: having a LVM (or not) volume group with only
> /dev/md0 and creating snapshots of that elsewhere while leaving
> the VG containing /dev/md0 undisturbed?
[...]
[replying to myself]
OK, I get it.
When one creates a snapshot, he changes the original block
device to be a "snapshot-origin" so that every write to the
device is forked into:
- copying the original block to the snapshot device(s) COW(s)
- writing to the original device.
So, if I've got the COWs on a failed disk, I suspect this might
degrade the performances or even stop the snapshot-origin from
working altogether wouldn't it?
I'll keep testing...
--
Stephane
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